1. Technical Field of the Invention
The present invention relates to a mobile terminal for a mobile communication system, and particularly, to a technique for suppressing a power consumption of the mobile terminal.
2. Description of the Prior Art
In the mobile communication systems, various techniques for transmitting a large amount of data such as image data within a short period of time have been researched and developed. For example, the data transmission rate of IMT-2000 as one of the next-generation mobile communication system is supposed to be 2 Mbps, in order to realize the highest-speed transmission ever in practical use.
In the mobile communication systems, higher transmission rate is desired. However, as the data transmission rate increases, processing loads on a base station and a mobile terminal increase, and the power consumption increases. In particular, a base station must communicate with a large number of mobile terminals at once at a high data transmission rate. Therefore, the apparatus for the base station becomes large-sized and expensive. In addition, since the electric power of the mobile terminal is supplied from a battery, an increase in power consumption is a crucial disadvantage.
Therefore, in the conventional mobile communication system, a low transmission rate is used, when an amount of information to be transmitted is small as in audio communication, while a high transmission rate is used, when an amount of information is large as in image data transmission. More specifically, when the mobile terminal starts calling, the mobile terminal notifies or requests a data transmission rate to be used in data transmission to the base station. The base station inspects whether or not a reception or processing of the signal from the mobile terminal at the requested data transmission rate is possible, on the basis of the capability of the base station and a present processing state. If the reception is possible, the base station permits a mobile terminal to transmit the signal at the requested data transmission rate. If the reception at the requested data transmission rate is not possible, the base station allocates a lower transmission rate for the mobile terminal. In this manner, in the conventional mobile communication system, communication is performed at a data transmission rate depending on an amount of information to be transmitted, thereby reducing a processing load on the base station so as to avoid the apparatus from being increased in size as well as to suppress the power consumption of the mobile terminals.
However, in a conventional mobile communication system, a user of mobile terminal directly notifies a designated data transmission rate to the base station. Therefore, for example, even if a residual amount of battery power of the mobile terminal is small, data transmission is performed at a high data transmission rate as designated by the mobile terminal. As a result, the residual amount of battery power is rapidly consumed. In the worst case, the battery runs out in the middle of data transmission.
There is disclosed a mobile terminal comprising a monitor unit for monitoring the degree of consumption of a battery, in JP1-120136 A (1989). However, the monitor unit merely monitors the degree of consumption of the battery in order to exchanging batteries timely. Therefore, the monitor unit is not aimed to suppress a power consumption.
Further, there is disclosed an invention for reducing the power consumption of a mobile terminal using a battery in a variable rate communication is disclosed, in JP7-38620 A (1995). However, this mobile terminal performs transmission and reception, not at various transmission rates, but at a constant data transmission rate.